Crude tall oil (CTO) is derived from the chemical pulping of woods. It is typically composed of a mixture of resin acids, fatty acids, sterols, alcohols, neutral substances, unsaponifiable matter and some non-acid materials. CTO can be distilled to obtain tall oil resin acids (TOR) containing more than 10 wt % of resin acid content. CTO may also be refined to tall oil fatty acids (TOFA), where the resin acid content is typically less than 10 wt %.
Tall oil pitch (TOP) is obtained as a nonvolatile residue from refining of CTO. The yield of TOP in the refining process may range from about 15 to 50 wt %, depending for example on the quality and composition of the CTO. TOP typically comprises neutral substances, free acids including resin acids and fatty acids, fatty acid esters, bound and free sterols, and polymeric compounds. Additionally metals, metal cations, inorganic and organic compounds including metal resinates and salts of fatty acids can be found in TOP. Said metal cations typically originate from wood and fertilizers.
CTO may be used as feedstock in hydroprocessing to produce hydrocarbons. However, as metals, compounds containing metals and other impurities are regarded as harmful to hydroprocessing catalysts, it is necessary to purify CTO before it enters the hydroprocessing catalyst beds. Typically CTO is subjected to one or more purifications steps, such as depitching, whereby a nonvolatile pitch residue containing high molecular weight compounds and contaminants is separated and in most cases disposed of by burning.
The utilization of TOP is limited, generally it is burnt, but some of it is used in asphalt emulsions, cement emulsions and printing inks.
Some methods for the purification of TOP are known in the art. However, to a significant extent valuable material present in TOP still cannot be utilized in an effective way.
There is an increasing need for biofuels, suitable as liquid fuels as such, particularly for transportation fuels, or compatible with said fuels. Biofuels are typically manufactured from purified feedstock originating from renewable sources, such as plant oils, animal fats, algal oils, fish oils, and the like. The common feature of these materials is that they are composed of glycerides and free fatty acids, and in many cases they are subjected to catalytic hydroprocessing as such. Usually, low quality feedstock containing contaminants, often of more heterogeneous nature, is regarded as more difficult to convert by catalytic hydroprocessing, and/or it requires more complicated equipment.
Despite the ongoing research and development of processes for the manufacture of liquid fuels, there is still a need to provide an improved process for producing hydrocarbons useful as liquid fuels or fuel blending components, from feedstock comprising contaminants and impurities.